This invention relates to surge suppressors which use metal oxide varistors (MOV) to prevent transient voltages in electrical distribution systems from reaching electrical equipment supplied by the system. The use of surge suppressors is common where sensitive equipment must be protected from transients superimposed on the line voltage. The invention provides for a signal to indicate that the protective function of the surge suppressor has been lost due to a varistor failure. The invention also prevents the establishment of an undesired low impedance connection between neutral and grounding circuit conductors as a result of MOV failures. The usual failure mechanism of an MOV is to go into a low resistance mode. This invention may be incorporated in an electrical receptacle.